Such a process is known from GB-A-1301646. This publication describes a process in which in a first reaction step a cyclohexanone oxime/tin (IV) chloride complex in the presence of .epsilon.-caprolactim-O-sulphonic acid is converted to an .epsilon.-caprolactam/tin chloride complex. Subsequently, the complex so formed is separated and in a second reaction step contacted with cyclohexanone oxime, in which .epsilon.-caprolactam and a cyclohexanone oxime/tin chloride complex is formed. The .epsilon.-caprolactam is recovered and the cyclohexanone oxime/tin chloride complex is recirculated to the first reaction step. The net result of all these reactions is that cyclohexanone oxim (alicyclic ketoximes) are converted to free .epsilon.-caprolactam (lactam) in the presence of a cyclohexanone oxime/tin chloride complex (tin chloride complex).
A disadvantage of this known process is that relatively many process steps are needed for preparing lactam. After each reaction step the desired product is separated off by, for instance, crystallization, which is not easy to accomplish for this group of reagents. In addition, the process is complicated by the introduction of tin(IV)chloride, a corrosive, moisture-sensitive reagent.